German Patent Application No. DE 10 2005 060 858 describes a method for operating a vehicle, in which an actual torque of a drive unit is influenced by a reference shaper. Sudden changes in load or switching operations may induce a jerking of the vehicle, in which the rotating engine mass and the rotating transmission mass typically oscillate with respect to the reduced vehicle mass. Other forms of oscillation are also possible. Conventional methods for reducing jerking oscillations are based on avoiding the excitation of the drive train by sudden changes in load. For this purpose, the torque requested by the driver via the accelerator pedal is low-pass filtered with the aid of reference shapers in the event of sudden changes or its rate of change is limited. This slows down the increase or reduction of torque. In addition, measures are taken at the time of zero crossing of the drive torque, for example when transitioning from coasting to traction mode. The associated zero crossing of the reaction torque generates a tilt of the engine-transmission unit in its support. In addition, mechanical tolerances and inaccuracies in the drive train are run through. For reasons of comfort, this transition should take place “softly,” which is achieved by limiting the gradient of the drive torque during its zero crossing. This is also the function of the reference shaper.
Conventionally, a rapid change in the torque of the electric machine requires a rapid change in the current; such rapid changes may shorten the service life of the electrical power source (battery). A very rapid drop in the torque of the internal combustion engine places a high heat load on the catalytic converter. At a low torque, the internal combustion engine works inefficiently. It is therefore advantageous either to operate the internal combustion engine at a high torque and to brake it using the electric machine as a generator, while current is being generated, or to shut off the internal combustion engine completely. The transition between these states is a situation in which the torque must be redistributed between the electric machine and the internal combustion engine.